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nesdev-template

A simple starter template for an NES project based around the ca65 assembler and linker, and GNU Make. It includes:

  • A working Makefile that builds a stub game ready for fleshing out.
  • A simple tool for automatically generating the Makefile-compatible build dependencies of each module by recursively scanning the assembly source for included files; the Makefile uses this by default.
  • Simple tooling to generate character ROM binaries from PNG or XCF sprite sheets as part of the make process. The bin/bmp2nes tools is by Damian Yerrick (see copyright notice there).
  • A PPU module with working reset/control routines, an NMI handler that implements a simple system for buffered writes of all key graphics data: OAM data (via DMA), Nametable data (via a write log), the scroll/mask/control registers. Provides routines for interacting with the buffers and NMI handler.
  • Some generic math macros derived from public domain code at 6502.org and cleaned up for ca65.
  • A random number generation module adapted from Damian Yerrick's code (see copyright notice in asm/random.s).
  • A simple controller input module (asm/joy.s, using "joy" as in "joy stick" or "joy pad").
  • A main module that ties these elements together into a simple program intended for NROM cartridges that displays a static graphical scene with a minimal "game loop" and some input handling, ready to be replaced and extended.

Usage

Optional prerequisite: The GIMP, for building graphics ROM data from XCF-format source assets. However, an intermediate PNG file is included in the repo in case you don't have gimp on the path.

  1. Fork this repo.
  2. Edit the Makefile to reflect the desired name of target iNES file, as well as the locations of tools like ca65 and emulators.
  3. Run make to build the target iNES file; run make mesen to do the same and run the Mesen emulator on the result.
  4. Begin modifying and extending the source code. As you add new modules, edit the Makefile to include their object file names (.o) in the definition of the OBJECTS variable, causing them to be linked into the target iNES file.

A note about includes and graphics

.include statements in your ca65 assembly code are automatically detected so that make knows which other files (usually .inc) the module object (.o file) depends on.

.incbin statements are also detected and mark binary files as dependencies of the module.

Make will attempt to create dependencies that don't exist (or are out of date) if it knows how, and the Makefile includes rules for creating binary CHR data from PNGs, and PNGs from Gimp XCF files. Therefore it is only necessary to put an XCF file foo.xcf in your repo as the "source" asset for some graphics, then .incbin foo.chr in your assembly code, and Make will automatically determine that it can satisfy the need for foo.chr by creating foo.png from foo.xcf and then foo.chr from foo.png, and that it must do so before assembling the module. See the example graphics files (chr/*.xcf) for the pixel layout and color format conventions expected by the graphics conversion tools.